


reciprocal

by whimsyappletea



Category: Vocaloid
Genre: Alternate Universe - High School, Childhood Friends, F/M, Fluff and Humor, Friendship, Friendship/Love, Humor, Male-Female Friendship, Matchmaking, Mathematics, Romance
Language: English
Status: Completed
Published: 2016-04-16
Updated: 2016-04-16
Packaged: 2018-06-02 14:18:35
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,351
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6569623
Author URL: https://archiveofourown.org/users/whimsyappletea/pseuds/whimsyappletea
Summary: <blockquote class="userstuff">
              <p>“Don’t we have anything better to talk about than a non-existent romance?”</p>
<p>—in which Gumi and Len are best friends, and Rin takes it upon herself to play data matchmaker. Lenrin, gumi.</p>
            </blockquote>





	reciprocal

**Author's Note:**

  * For [](https://archiveofourown.org/gifts).



> oooh i remember being swamped by assignment deadlines and having, like, three rewrites before finally settling on this version :'D considering how stressed and low on sleep/happiness i was im still surprised how well it turned out in the end sweats ;;
> 
> inspired by real life classmates and a tumblr post by ughsos (currently jax) that had been circulating around. this was written as a happy day of birth fic to **Piriluk** \- i still love you and never forget youre awesome heheh
> 
> fun dynamics with len+gumi, and the usual lenrin applies – enjoy!

.  
.  
.

Rin has known Megpoid Gumi for exactly one year, fifteen days, nine hours and thirty-five minutes. The green-haired girl is a constant variable in her high school life thus far, with a steady, practical personality and well-defined routines that are predictable and easy to remember.

Data tells you everything you need to know. It’s factual, objective and vital to success. Sure, sometimes you have to update it to keep it up-to-date, but at least data doesn’t lie.

If there’s anything Rin hates about data, it’s _unpredictability_ —and Gumi’s best friend of roughly ten years is the epitome of an irregular variable.

“Shimoda, answer to question seventeen?”

The blonde doesn’t even look up from her notebook as she says, “Ten factorial.”

Hmph. Easy as the mathematical symbol Pi.

“What,” a whisper hisses from her left. “How did you even _get_ that?”

Rin raises an eyebrow, turning to look at the boy beside her. Despair is an expression that doesn’t look well on him, she notes. “You use the BODMAS rule, Kagamine,” she states unhelpfully.

He stares long enough to make her uncomfortable, before reaching over to mess with her short locks. “You’re too smart,” he mourns, a soft, unreadable glint in his eyes. “How did I end up sitting next to the genius again?”

She blinks, too thrown to scold him about her hair or provide a snarky comeback. The only thought that comes to mind is: Kagamine Len, you _goddamn_ irregular variable.

.

**reciprocal**

_his eyes see right to my soul, i surrender self-control—  
catch me looking again,  
falling right into my plan._

.

“Are you blind? That packet was labelled ‘sugar’!”

“I _know_ , that’s why I took it!”

“TWO TEASPOONS, GUMI. NOT TWO _SPOONFULS_.”

“Bah, I’m sure it means the _same thing_ —”

It’s home economics right now, and Rin can’t help but glance over covertly from time to time, observing the interactions between Gumi and her best friend. The boy has bumped her aside with his hip to shoo her away from adding more sugar, while the girl is clinging to his back with the skill of a koala bear, insisting that they should add _more_.

The sugar horror aside, Rin has long since accepted the fact that Gumi comes with a sort of packaged deal: if you want to be friends with her, you have to learn to deal with the cumbersome pest that is Kagamine Len. This unwritten rule has been set up ever since the pair became friends back in elementary school.

Reportedly how they’d _become_ friends in the first place is interesting too—Kagamine had jeered that girls were weak and couldn’t punch for nuts, but he’d gone down like a champ almost immediately after Gumi nailed him right in the face.

A flurry of phone calls and a couple of hours later, the principal had decided to settle the issue on both ends by requesting Gumi to apologize. Kagamine wouldn’t have any of it, though—he’d exclaimed to his mother, as quoted by the green-haired girl herself, “But she proved me _wrong_ , ma! That’s _so cool_!”

Looking at present-day Gumi and her best friend, Rin certainly doesn’t doubt the credibility of this incident—the girl still has no clue about the sheer power she has in those slender limbs of hers, though.

“Wow, those look _good_ ,” Kagamine says, leaning in to peer at the frosted cookies on her plate. The blonde jerks away, startled; his warm breath had been right next to her ear.

“Better than ours, at any rate,” Gumi chimes in, looking sulky as she props her chin on his shoulder.

The boy clicks his tongue, picking up a cookie to wave it in front of her mockingly. “See, Gumi, _this_ is why you don’t put so much sugar. Or eat, like, eighty percent of the cookie dough.” He takes a bite, and his eyes grow round in awe. “Holy _shit_ , I think I’m in heaven.”

Before Rin can react, he drops the half-eaten cookie to take her by both hands. The boy looks her square in the eye, his expression perfectly smooth and sombre, and says, “Rin, _please marry me now_.”

“You just took a bite of a cookie and dropped it back into the unsullied cookies,” Gumi complains in the background. “That’s a _party foul_ , Len, what the hell—”

“Shut _up_ , Gumi, can’t you tell I’m trying to have a serious moment here—”

“ _No_ , you take your goddamn cookie away before I drop-kick you into next Friday, you _asshat_ —”

Rin blinks, slipping her hands away from the boy. She’s still trying to process what had just occurred as the pair continue to bicker about the importance of uninterrupted marriage proposals and unwanted saliva exchanges.

.

“We’re just friends, guys. _Just friends._ ”

But that’s what you always say, Rin thinks absently, picking at the contents of her lunchbox as Gumi scoffs playfully at something mentioned by their fellow classmates. Today’s lunch is highly appetizing, with octopus-like sausages and carrots and potatoes in her own homemade curry udon, but Rin is more interested in the gossip happening right then.

“Are you suuuure?” asks one of the girls, giggling good-naturedly. “I mean, you two _are_ pretty close. You would look really cute together, I swear by my favourite spring onions!”

“Can it, Miku,” Gumi laughs, a grain of rice stuck to the corner of her mouth. The girls would point this out if it were anyone else, Rin knows, but the green-haired girl does not care much for her appearance. “Don’t we have anything better to talk about than a non-existent romance?”

The conversation moves on from there—Gumi has a talent for switching topics with ease, which is probably why she gets along with nearly everyone—but Rin continues to dwell on the “just friends” comment. Because... why _not_?

They _would_ look good together, as Miku had pointed out. The height factor is definitely there, the blonde muses, jotting this down in her handy notebook. The chemistry is strong, and so are their public displays of affection. Becoming a couple is more than plausible for them, so—maybe they’re missing something.

Maybe... a push in the right direction?

Rin isn’t a meddler. As a data-collector, she typically sits to the side—usually beside Gumi, or sometimes Kagamine on a good day—and observes from afar. It ensures objectivity, keeps her facts grounded and cross-checked for accuracy.

But Gumi is a good person—and a good friend, at that.

It wouldn’t hurt to help the girl find happiness, the blonde decides. Even if she _does_ have to deal with the highly dislikeable irregular variable.

.

“Kagamine’s quite the catch, isn’t he.”

The green-haired girl turns to stare at her, wide-eyed, and Rin bristles. “Wh—what’s _that_ look for?”

“Nothing,” Gumi says, slow and mildly incredulous. It’s free period, and the library is full of students trying to cram last-minute information into their panicked minds in preparation for the upcoming exams. “I just... didn’t expect that. From _you_ , of all people.”

Rin frowns, intent on pursuing that line of thought, but her friend interrupts before she can. “What makes you say that, Rin?”

Ah, right. The mission. “Well—I mean, come on, just look at him.”

Kagamine is sitting at one of the tables nearby, looking fairly at ease despite being flanked on all sides by a clique of pretty upperclassmen girls. Some are playing with his hair, others touching his shoulders, his face, the strong line of his jaw. One even has the audacity to sit on his lap.

Gumi, however, doesn’t even bat an eyelid, and resumes highlighting her Biology notes. “Hm? What about Len?”

It’s even less of a reaction than Rin had expected.

A shrug, more calculated than careless. “I don’t know—aren’t you the least bit concerned that he’ll end up a pimp when he grows up?”

She snorts, as if the mere notion of such an idea was simply ludicrous. “ _Please_ , he doesn’t have what it takes to be a pimp. He’s just... kind. _Too_ kind, even.”

Hm. Gumi has a point there. Rin taps her pencil against her chin over a thoughtful pause, before jotting this down. If there’s anything about boys that attracts girls like bees to honey, it’s kindness—to be someone cool and dependable, to be a true gentleman.

Kindness can also be a double-edged sword, though, the blonde muses. It converts you into public property, and just about anyone has the right to talk to you, to touch you. Definitely going to be a problem when he lands himself a girlfriend—especially if the girlfriend’s the type who gets jealous easily.

“Yeah, that’s true, but she’s not that type of girl. I’m sure of it.” Gumi smirks at her confused blinking for a moment, before asking, “Say, do you have the answer sheet for this practice paper? I think I lost mine somewhere...”

She hadn’t realized she’d voiced that particular sentiment aloud. But how can the green-haired girl be so sure of that... unless she already knows that she _herself_ won’t be such a person as Kagamine’s girlfriend?

As Rin hands over her copy of the solutions, her mind is racing to generate new ideas stemming from Gumi’s vague yet promising answer.

.

“Ooh, whatcha writing there?”

Rin slams her notebook shut with a loud _BANG_ , clutching it to her chest protectively. She hadn’t expected his arrival at all, that _goddamn_ irregular variable—how did he know she was still in class, anyway?

She would’ve pinned the intruder with a death glare, if not for the fact that he’s using her head as an arm-rest. Instead she settles for an improvised, “Planning out my schedule for next month.”

“Must be some schedule to make you react like that.” Kagamine whistles, waggling his eyebrows suggestively. “If it involves lots of wild romping, can I watch?”

She flushes pink at the notion, completely flabbergasted, and he laughs outright, eyes glinting with that soft, unreadable look that irritates her to no end. “How adorable,” he coos, prodding at her cheeks teasingly. “Is wittle Rin-Rin getting _embarrassed_?”

“Embarrassed for your Neanderthal way of thinking,” Rin blusters, lifting her chin at a defiant angle and narrowing her eyes at him. “What are you, twelve?”

“Yeah, a twelve out of ten in your eyes,” he cackles, obviously relishing in her reaction to his teasing. This is the main reason why Rin dislikes bantering—she, for the lack of a more diplomatic word, utterly _sucks_ at it—and now desperately wants to throw something hard at him, preferably a brick or a punch from Gumi.

As if on cue, the green-haired girl herself appears, kicking Kagamine right where it hurts the most: the shin. He’s not able to dodge in time; with a sharp yelp of pain, he clutches at the spot that’s most likely to bruise later and collapses to the floor in a heap.

“Can you _be_ any more obvious?” Gumi demands, hands akimbo as she looms over his prone form. The boy moans theatrically, whining about domestic abuse and crotchety carrot-loving ladies who don’t know their own strength.

Rin, on the other hand, is blinking slowly. “Obvious?” she echoes, but her green-haired friend has launched into a full-blown lecture about idiots who don’t know when to quit and shut their traps.

.

The blonde can barely believe what she’s hearing. “Come again?”

“Len likes someone,” Gumi repeats, giving her an odd look. “You mean I’ve never told you this before?”

“No, never.” This is a _complete_ game-changer—had Rin known, she would’ve factored it in when devising plans for the pair to get together. She’d simply assumed that both of them were not aware of each other’s feelings... yet apparently Kagamine is.

What an interesting turn of events. The blonde’s itching to scribble down all the new possibilities in her notebook, but doesn’t want to risk raising any suspicions. It would look pretty strange to whip it out in the middle of dinner at the neighbourhood café, after all.

“Meh, I thought it was obvious, anyway,” Gumi mutters, slurping at her extra-large cup of carrot juice. “Len’s, like, the most transparent dude I know.”

Rin furrows her eyebrows, perplexed. She’s been observing for a while now, and the most romantic thing she’s ever seen Kagamine do is to throw the girl over his shoulder like a sack of potatoes and whisk her away to the infirmary when she’d sprained her ankle, and—even _that_ isn’t particularly obvious.

They do touch a lot, though. Gumi is sensory-oriented, and tends to be a lot more ‘touchy-feely’ with people than most are comfortable with. Rin herself has to stop her from tugging her hair and poking her hips and invading her personal bubble sometimes. Kagamine, on the other hand, is laidback enough to let her do as she pleases.

Maybe that’s what Gumi means by ‘transparent’, the blonde thinks. As a precaution, though, she makes a mental note to pay closer attention to Kagamine’s mannerisms from now on.

.

Rin wakes up to the sensation of a wet cloth dabbing across her forehead. She pulls the blankets tighter around her, feeling her body ache all over and her throat burn like fire had scorched her lungs. God, she _hated_ falling ill—what are the odds of catching a flu bug right at the start of the holidays, anyway?

“Oh, you’re awake,” says a voice somewhere above her, and she’s not sure why it sounds so familiar. The blonde squints against the dizzying lights overhead, barely making out a shadowy figure shifting closer to her. “At least your fever’s gone down a bit.”

“Gumi,” she manages to croak, grimacing at the scratchiness of her voice. Her parents are working hard to make ends meet and don’t have time to look after their bedridden daughter, so they usually ask Gumi to help out. She’s the first and only person outside of her family to have a spare key to her house.

“I, uh...” A warm hand reaches out to brush her sweat-soaked bangs away from her eyes, the action far gentle than expected. “Just—go back to sleep, Rin. You need to rest.”

Rin’s head is pounding too much for her to say anything else, so she lets her heavy eyelids flutter shut, drifting off into a deep, dreamless sleep.

The next time she wakes up, she’s feeling way better and looking a lot more alert. Gumi is there with some surprisingly tasty chicken soup and warm porridge, chiding her for forgetting to take care of herself. For some odd reason, warmth is the only thing she remembers about that afternoon.

.

“Gah, I give up!” Kagamine cries, dropping his head lightly against Rin’s shoulder in defeat. It’s just the two of them in the classroom after school, since Gumi had just left for a meeting with a couple of classmates for their Biology project. “I’m done with life. Wake me up when high school ends.”

She stills her pen, frowns down at the added weight. Contemplates murdering him, but thankfully chooses to leave him be for now. “It’s just the convergent series of reciprocals.”

“I don’t care if it’s convergent or divergent,” the boy grouses into her arm. “Question marks should just _stay_ question marks, without all these voodoo ‘ _n_ ’s and ‘ _k_ ’s that pop out of freakin’ nowhere.”

“It’s not that bad,” is all she says, before they lapse into comfortable silence. Rin has never been particularly close to Kagamine, but he’s rapidly becoming more and more tolerable as of late.

Then again, Gumi is strangely prone to leaving them alone together a lot these days—from lunches to group projects to heading home to look after her siblings, she’s far busier than the schedule Rin has recorded in her notebook.

It’s almost as if—oh.

_“Yeah, that’s true, but she’s not that type of girl. I’m sure of it.”_

Oh, no.

_“Can you be any more obvious?”_

No, it can’t be.

_“Len’s, like, the most transparent dude I know.”_

Her data doesn’t lie, but this is just— _inconceivable_.

Right?

“Rin? Earth to Rin, what’s up with you?” Kagamine lifts his head to look at her, his eyes holding that soft glint as usual. She’d always brushed it off as unreadable. God, she’s so _dumb_. “Oi, your face is really red, are you alright—?”

“It’s me, isn’t it.”

“What?”

“I’m the girl you like,” Rin says blankly.

As if she’d dropped ten tons of lead onto him, the blond tenses, a blush making its way up his throat painfully slow. “Psshh, no way! What makes you... say... that...” he trails off when he notices her face draw closer and closer, and tries to lean back with a nervous chuckle. “Rin, this is—I, uh—”

“You were there,” she realizes, instantly cross-matching the intonations of his speech interjections to the one from her hazy, illness-clouded memory. “At my house. Gumi let you in. The porridge, the soup—they were all from _you_.” The missing pieces of the puzzle are finally coming to her, starting to fall perfectly into place.

Why hadn’t she noticed it before?

“I, uh,” Kagamine tries again, his fluster growing more evident the more he tries to hide it. Oh, how the tables have turned. “It’s just—I can’t—” he chokes when Rin cups his cheeks in her hands.

“Do you like me,” she asks, not one to waste time or words. “A simple yes or no would suffice.”

He opens his mouth, closes it. Flounders for a little while longer, before finally murmuring in a tiny, terribly abashed voice, “Yeah. Yeah, but do you... uh...”

Rin blinks, a little taken aback by his uncharacteristic shyness. They really are _just friends_ , after all; he definitely wouldn’t be this incoherent around Gumi, or any of those girls who flock around him in droves.

Kagamine Len, you _goddamn_ irregular variable, she smiles wryly. She can’t believe she’s saying this, but—

“Yes, you idiot, I like you too.”

.

Rin has known Megpoid Gumi for exactly one year, one-hundred-and-eighteen days, fifteen hours and forty minutes. The green-haired girl is a constant variable in her high school life thus far, with a really mean right hook that can probably shatter a man’s pride and a similar temperament to boot.

Data tells you everything you need to know. It’s factual, objective and vital to success. Sure, sometimes you end up a _little_ unaware of things that should be glaringly obvious to you, but at least data doesn’t lie.

If there’s anything Rin hates about data, it’s _unpredictability_ —and Gumi’s best friend of roughly ten years is the epitome of an irregular variable.

Through Kagamine Len she has learnt that data is arbitrary in its own way: it cannot predict the heart, after all.

.

_yeah, you show me good loving,_  
make it alright—  
need a little sweetness in my life. 

.  
.  
 **omake:**  


“Wait,” Len says suddenly, jerking his head up to look at the girl beside him. After all that’s been confessed and realized, they’re packing up to head home for the day. “Wait, how did you know the soup and the porridge were from me?”

The blonde shrugs, unperturbed. “At first I’d assumed Gumi had gotten them from some random coffee-shop, but now that I think about it, they were too delicious to be store-bought. So that left you.”

To Rin’s surprise, colour spills across his cheekbones once more. In an attempt to play it off casually, he shoots back, “W-well, why not Gumi?”

She throws him a peculiar look, her eyebrows raised and lips curved. Says, in a blunt, matter-of-fact manner, “You and I both know that Gumi can’t cook to save her life.”

“Wow, Rin. Wow. _RUDE._ ”

Len jumps in surprise at the sudden addition to their conversation, whipping his head around to stare daggers at his best friend. It doesn’t work as well as it should, considering the blush on his face that seems to have worsened. “Since when were _you_ here?!”

Calmly placing her pencil case into her book-bag, Rin mumbles, “Probability of Gumi eavesdropping from the start: one hundred percent.”

A pause, and then:

“ _MEGPOID FREAKIN’ GUMI._ ”

.  
**owari.**  
.  
.  
.

**Author's Note:**

>  **disclaimer:** i do not own Vocaloid, Britney Spears’ _Radar_ , or Maroon 5’s _Sugar_.


End file.
